Open circuiting arrangement for commutator brushes



March 13, 1951 H. T. LANG 2,545,365

OPEN CIRCUITING ARRANGEMENT FOR COMMUTATOR BRUSHES Filed April 27, 1950 Inventov: Henry T. Lan

H is Attovney.

Patented Mar. 13, 1951 OPEN CIRCUITING ARRANGEMENT FOE CGMMUTATOR BRUSHES Henry T. Lang, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application April 27, 1950, Serial No. 158,526

5 Claims. 1

My invention relates to dynamoelectric machines and particularly to commutator brushes for such machines.

In Patent No. 2,029,171 issued January 28, 1936 to August F. Lundquist entitled Brush for Mo- 1 tors and Generators a type of commutator brush is disclosed which consists of a circular or diskshaped body of carbon or other brush material mounted to turn on a central stud. A coiled spring urges the brush rotationally against the commutator, and as the brush wears the Wear will be taken up by the rotation of the brush through the action of the spring. The surface of the brush is therefore worn to a smaller diameter by action on the commutator. A large amount of material is thus available to be used and worn away without need for the commutator to occupy as much space as if a straight brush were used. My present invention is particularly useful as an improvement over this type of commutator and may be used wherever the direction of wearing movement of the commutator brush is generally tangential rather than radial to the outer surf ce of the commutator.

My invention is designed not only to urge the brush against the commutator but also automatically to remove the brush from contact with the commutator when the brush is substantially worn. This prevents sparking or burning between the brush and the commutator which might damage the commutator and related dynamoelectric machine construction. Removal of the brush opens the circuit between the brush and commutator so that sparking is not continued.

The principal objects of my invention are met by providing the end of the wearing edge of the brush with a cut-away portion or notch, and by providing a stop on the brush to limit its movement so that when the edge of the brush has been worn away to the notch the brush will move further in the same direction so that the notch is opposite the commutator, thus breaking the circuit between brush and commutator because the brush surface is now no longer in contact with the commutator.

Other objects and the details of a preferred form of my invention will be clear from the f0llowing description and claims taken with the accompanying drawing in which is illustrated an example of dynamceiectric machine embodying the present invention and incorporating my improved brush construction.

In the drawing Fig. l. is a sectional view through a part of a motor, showing the commutator, the brush and a support for the brush; Fig. 2 is a plan I later appear.

view of the commutator and brush of Fig. 1 with the brush in its starting or unworn position; Fig. 3 is a View similar to Fig. 2 but showing the brush in nearly completely worn position; and Fig. 4 is a still further view showing the brush in its completely Worn and open circuiting position.

A motor according to my invention may have the usual armature I mounted to rotate on a shaft 2 and carrying a commutator 3. The brushes which engage with the commutator are mounted on a stationary part of the motor frame (not shown). I have chosen to show a bracket 4 for supporting the single brush illustrated in the drawing, it being understood that this constructicn may be repeated in the usual fashion.

The bracket 3 not only supports the brush but asc serves as a conductor leading to the brush. Threaded or otherwise suitably secured to the bracket is a supporting and conducting post 5 which is made preferably polygonal or non-circular in horizontal section for reasons which will Fitting closely on the outside of post 5 and having a cylindrical outer bearing surface is a bearing sleeve or tube 5 which has a rotatable fit within the bore of the disk-like or circular brush 1. Because of the close fit between the outside of the non-circular post 5 and the inside of the tube 6, these members will not rotate relative to each other, but the brush 1 wi l be capable of rotation outside the sleeve 6.

The outer surface of the brush 7 will be made of a suitable width for application to the commutator and in the under surface of the brush a recess 3 is provided for a coiled spring 9. The .Z end of the coiled spring is seated or otherwise secured to the sleeve 5 as in the slot or groove ill. The outer end of the coil spring may be seated or otherwise secured to the brush 1 within the cavity 3 as in the slot I i. It is understood that the spring coil is wound up sufficiently tight to have power to rotate the brush through a complete revolution about the axis of the sleeve 5 and also to give the proper pressure against the commutator to insure good carbon brush life.

The outer edge of the brush is generally cylindrical or circular in form as indicated at [2, the ci cumference of this circle or cylinder, to a depth indicated by the dot-dash lines W, constituting wearing or useful portion of the brush. Obviously, that portion of the brush to the depth In. arked W should be made of carbon or other satisfactory brush material. The remainder of the brush simply acts as a conductor and may be made of any suitable material for that purpose 3 although I have shown the entire brush made of carbon. In a manner readily understood from the above description and by reference to the drawing, the brush will be gradually Worn away around its circumference until practically the entire periphery of the brush will have been used.

It should be noted that the portion of the brush which is worn away moves in a position or direction tangent to the circumference of the commutator. That is, in the arrangement shown in the drawing, the circle formed by the commutator 3 and the circle formed by the worn brush will be tan ent to each other. Although the axis of rotation of the commutator and the axis of rotation of the brush have both been shown as vertical and parallel to each other, it

is obvious that the brush could be arranged to rotate about an axis at right angles to the commutator axis of rotation. In this case the circles of the commutator and of the worn brush would still be tangent, but in planes at right angles to each other. Also, it hould'be noted that according to one aspect of the present invention the brush need not move in a rotational path at all but in a straight path, with a straight brush, if the wearing portion of the brush engages the commutator at a tangent to the circumference of the commutator. Usually a commutator brush engages the commutator radially, or nearly so.

With the tangential engagement of the brush commutator, the present invention may be utilized. Stated in its simplest terms, provision is made so that when the end of the wearing surface of the brush s reached and the spring pressing the brush urges it further in this same direction, the brush will come up against a stop, cutaway portion or recess on the brush will be located opposite the commutator, forming a gap between the brush and commutator.

In the form shown in the drawing, the stop for the brush is provided through the medium of a stop washer it havin an extension or lug i i which extends in the path of rotational movement of astop pin it"; which is soldered or otherwise suitably secured to the brush 2'. This stop pin ['5 may be a stiff end. on a flexible electri cal lead i6, as shown in the drawing, the other end of the lead being fastened, as by a suitable terminal screw ii, to the conducting and supporting post The washer i3 is held against rotation on the post 5 because the inside of the washer fits the non-circular form of the post and maybe clamped securely on the post as by the nut it. The circuit breaking gap or recess is indicated. by the number iii, this sector of the circumference being cut away to a depth greater than the depth of the line of wear W and being so located that when the pin or stop i5 comes into engagement with the extension M at the end of the rotation of the brush, the stop [5 will hold the gap 69 opposite the commutator in the position shown in Fig. t. Thus when the brush is completely worn it will have turned somewhat less than 360 and an open air gap will be presented between the commutator and the brush, avoiding burning or damage to either the brush or the commutator.

The direction of the arrows in Figs. 2, 3 and 4 show the preferred direction of rotation of the commutator and of the brush. It will be noted that the direction of movement of the brush is opposite the direction of rotation of the corninutator. However, the di ections of movement might be made to coincide if desired.

A circular brush according to the preferred form of my invention should be capable of lon life and be free from sticking, chattering or squealing. The contact pressure will be substantially uniform throughout the entire wearing life of the brush and when the useful life has been spent, the brush contact surface is automatically removed from contact with the commutator without the necessity of addition of complicated parts or mechanisms.

As will be evident from the foregoing description, certain aspects of my invention are not limited to the particular details of construction of the example illustrated, and I contemplate that various and other modifications and applications of the invent-ion will occur to those skilled in the art. It is therefore my intention that the appended claims shall cover such modifications and applications as do not depart from the true spirit and scope of my invention.

What I claim new and desire to secure by Letters Patent of the United States is:

1. In a dynamoelectric machine, a commutator having a circular contact surface, a generally circular brush with a peripheral wearing surface mounted for rotational movement and wearing about a circle tangent to circular surface of commutator, said wearing surface having a recess therein at one end a stop so limiting movement of said brush that said recess is moved and located opposite the commutator circle when the brush is worn to said whereby an open is provided between the commutator and brush when the brush becomes worn.

2. In a dynamoelectric machine, a commutator having a circular contact surface, a generally circular brush with a peripheral wearing surface mounted for rotational movement wearing about a circle tangent to said circular surface of said commutator, resilient means urging said brush for movement in said rotational direction, said wearing surface having a recess therein extending below the depth of the worn portion of said brush and a stop so limiting movement of said brush that said recess is moved and located opposite the commutator circle when the brush is worn to the end of said wearing surface, whereby an open gap is provided between the commutator and brush when the brush becomes worn.

3. In a dynamoelectric machine, a commutator having a circular contact surface, a brush supporting post, a generally circular brush on post with a peripheral wearing surface mounted for rotational movement and wearing about a circle tangent to said circular surface of said commutator, said wearing surface having a recess therein at one portion of said periphery, resilient means urging said brush toward progressive rotational wearing movement about its periphery, and a stop so limiting movement of said brush that said recess is moved and located opposite the commutator circle when the brush is worn to said recess, said stop comprising a pin on said brush and a cooperating lug on said post extending in the path of rotational movement of said pin.

4. In a dynamoelectric machine, commutator having a circular contact surface thereon, a brush supporting post. a generally circular brush rotat ably mounted on said post. a peripheral wearing surface on said brush, said wearing surface having a recess therein in one portion of said periphery, an electrical lead extending from said post to said brush and secured to the to form a stop so limiting movement of said brush that said recess is located opposite the commutator circle when the brush is worn to said recess.

5. In a dynamoelectric machine of the type having a commutator, a generally circular brush of a given radius rotatably mounted to bear and Wear progressively circumferentially against said commutator, the worn portions of said brush having a radius equal to that of a circle tangent to the commutator, that improvement in removing the brush from contact with the commutator when substantially the entire circumference of the brush becomes worn comprising a stop limiting the rotational movement of said brush to somewhat less than 360, and a sector on said brush of a radius less than that of a circle tangent to the commutator, said stop being located to position said sector opposite said commutator when said brush becomes worn.

HENRY T. LANG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

